1. Field of the Invention
The present invention relates to a digital data reproducing device, and more specifically, a digital data reproducing device that is capable of controlling degradation level of digital data according to number of reproduction times, a time limit for reproduction, or copy operation, and of contributing to copyright protection, in reproducing devices for reproducing digital data such as video, audio in particular.
2. Description of the Related Art
Japanese Patent Application Laid-Open (JP-A) No. 2006-279428 (Patent Document 1) discloses a compressed data scrambling delivery device with means for applying a plurality of scrambles to encoded data, and embedding into scrambled compressed data a signal for discriminating the applied scrambled signals as digital watermark data. When reproducing the data, the device determines a method of descrambling based on the embedded signals as the digital watermark, and descrambles the compressed data using the method.
JP-A No. 2004-030630 (Patent Document 2) discloses a method of a content provider specifying a quality degradation policy or a quality degradation specification model for every digital data, wherein if the digital data is copied or moved, the copied data will be degraded according to the policy or the model.
JP-A No. 2001-067794 (Patent Document 3) discloses means for holding in a header of content data a reproducible period, number of reproducible times, and number of reproduction times, and for determining whether or not to reproduce depending on the reproducible period or the number of reproducible times.
JP-A No. 2002-006885 (Patent Document 4) rewrites content of digital data based on condition information showing a time limit for reproduction when the time limit for reproduction reaches, and notifies that the time limit for reproduction is approaching, by doing this rewrite whenever reproduction is performed.
JP-A No. 2006-127656 (Patent Document 5) discloses means for mixing noise into content data limited in number of reproduction times, as the number of reproduction times approaches the limited number of reproduction times, and for causing the data to degrade in stages.
In an approach of the Patent Document 1, as it is necessary to have a key corresponding to each scramble when a plurality of scrambles are applied to single digital data, amount of data to be embedded as digital watermark increases, thereby possibly degrading quality of digital data.
In an approach of the Patent Document 2, as it is necessary to specify a quality degradation policy for every digital data, operation cost involved in delivery of content of a content provider will be enormous. Furthermore, the approach does not disclose a method of degradation associated with number of reproduction times of digital data.
By contrast, although the Patent Documents 3, 4, and 5 disclose a mechanism of degrading data as number of reproduction times increases, based on the number of reproduction times and information related thereto, data itself flows normally in any case. Thus, if any normal reproducing device other than those disclosed in these Patent Documents is used, there is a problem that desired operation cannot be achieved because information of number of reproduction times cannot be interpreted.
In addition, in all of prior arts, it is not assumed to gradually refine degraded digital data according to the information on the number of reproduction times.